P422: OMIPALISIB, A DUAL PI3K/MTOR INHIBITOR, TARGETS MITOCHONDRIA AND IMPAIRS OXIDATIVE PHOSPHORYLATION IN ACUTE MYELOID LEUKEMIA
Authors: C.-Y. Tseng, C.-Y. Kuo, Y.-H. Fu, H.-A. Hou, H.-F. Tien, L.-I. Lin
Journal: HemaSphere (2022)

Background: Mitochondria play a central role in cell metabolism. Recent studies explored mitochondrial alterations contributing to metabolic vulnerability in myeloid leukemia cells may considered as therapeutic targets. We previously reported that omipalisib, a PI3K/mTOR dual inhibitor, could significantly inhibit the growth of myeloid leukemia cells and impair their mitochondrial respiration. However, the precise mechanism of the mitochondria dysfunction in response to omipalisib is still not fully studied. Aims: To explore the mechanism of the mitochondria dysfunction in response to omipalisib. Methods: OCI-AML3 and THP-1 myeloid leukemia cell lines were used in this study. Omipalisib (GSK2126458) and another PI3K/mTOR dual inhibitor gedatolisib (PF-05212384) were used. Flow cytometry was used for mitochondrial analysis. RNA-seq was performed by using an Illumina NovaSeq 6000 platform. Differentially expressed genes (DEGs) between control and omipalisib (or gedatolisib) were identified by EBseq with a threshold of p ≤ 0.05. The mRNA, nuclear and mitochondrial DNA quantification were measured by using QuantStudio 3 Real-Time PCR Systems. The parameters of mitochondrial respiration were analyzed by using the XFe 24 extracellular flux analyzer. Results: We demonstrated the anti-proliferative effect of omipalisib and gedatolisib on a panel of AML cell lines with different genetic backgrounds. OCI-AML3 cell lines had significant response to omipalisib and gedatolisib with IC50 of 17.45 nM and 153.38 nM, respectively. Subsequently, the transcriptome analysis of 50 nM omipalisib or 200 nM gedatolisib-treated OCI-AML3 cells were analyzed. Compared to DMSO-treated, a total of 1199 (595 upregulated and 604 downregulated) and 326 (218 upregulated and 108 downregulated) DEGs were identified in the omipalisib-treated cells and the gedatolisib-treated cells, respectively. Gene set enrichment analysis (GSEA) indicated that both omipalisib and gedatolisib could suppress “E2F targets”, “Myc targets”, and “G2M checkpoint”, and trigger “TNFα signaling via NFκB”, and “Inflammatory response”. Of them, we found that omipalisib had more significant effect to inhibit “Oxidative phosphorylation” (NES: -2.01) than gedatolisib did (NES: -1.40), especially mitochondrial biogenesis and amino acid metabolism-related pathways. Omipalisib had an inhibitory effect on the mitochondrial basal respiration rate and maximal respiration. Further analysis revealed quantitative reverse-transcription PCR analysis revealed that both omipalisib and gedatolisib could potently suppress serine synthesis (PHGDH, PSAT1, PSPH), glycine synthesis (SHMT1/2), and tetrahydrofolate cycle-related genes (MTHFD1/2) at the transcriptional level. On the other hand, rather than gedatolisib, omipalisib could significantly inhibit expression of glycolysis-related genes (GLUT1, HK2, PKM2, and LDHA) as well as mitochondrial biogenesis-related genes (PPARGC1B, TFAM, and NDUFS6). In addition, omipalisib could strongly decrease mtDNA and mitochondrial mass. These results suggest that omipalisib could suppress the mitochondrial biogenesis through alternative mechanisms, including but not limited to PI3K-AKT-mTOR signaling. Summary/Conclusion: Rather than gedatolisib, omipalisib could significantly inhibit mitochondrial biogenesis and suppress the respiration of mitochondria in myeloid leukemia cells. Our results indicate that omipalisib could suppress cell proliferation not only through PI3K-AKT-mTOR signaling but also via impairing mitochondrial biogenesis. This information may be potentially suitable for future clinical applications.